The Calgary Arm is an ultra-low-cost upper-limb prosthesis designed to be assembled from widely available materials. It operates on the principle of a jamming gripper. If you have seen a vacuum packed bag of rice, ground coffee, etc, you have probably noticed that it remains hard until you puncture the package and let air in, at which point the contents can flow and the bag can easily be reshaped in your hands. This is because external air pressure tightly packs the individual grains together so they jam and can’t slide past one another. When the vacuum is released, so is the jamming effect, and the grains can flow readily. A jamming gripper makes use of this principle when the outer layer (in this case a balloon) deforms to adjust to the shape of whatever it is pressed against, and then a vacuum is applied (in this case via a reversed …
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